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Abstract:

The present disclosure relates to solvent surveillance in heavy oil
production. A method includes the steps of measuring an amount of a
native bitumen marker (NBM) in a heavy oil, measuring an amount of the
NBM in a recovery-aid solvent, measuring an amount of the NBM in a blend
including the heavy oil and the recovery-aid solvent, and applying a
blending model to determine a fraction of the recovery-aid solvent in the
blend.

Claims:

1. A method of solvent surveillance, comprising the steps of: (a)
measuring an amount of a native bitumen marker (NBM) in heavy oil; (b)
measuring an amount of the NBM in a recovery-aid solvent; (c) measuring
an amount of the NBM in a blend, wherein the blend comprises the heavy
oil and the recovery-aid solvent; and (d) applying a blending model to
determine a fraction of the recovery-aid solvent in the blend.

2. The method of claim 1, wherein the blending model is at least
partially described by formula: the fraction of the recovery-aid solvent
in the blend=(NBMo-NBMb)/(NBMo-NBMras); wherein NBMo is the amount of the
NBM in the heavy oil, NBMb is the amount of the NBM in the blend, NBMras
is the amount of the NBM in the recovery-aid solvent.

3. The method of claim 2, wherein the fraction of the recovery-aid
solvent and the amounts of the NBM are all measured in a unit selected
from the group consisting of weight fraction, mole fraction, volume
fraction, parts per million by volume, and parts per million by weight.

4. The method of claim 1 wherein the blend further comprises a
separation-aid solvent and the method further includes the step of
determining a fraction of the separation-aid solvent in the blend,
wherein: the blending model is at least partially described on a
separation-aid solvent free basis by formula: the fraction of the
recovery-aid solvent in the blend=[NBMo-NBMb*(1/(1-SASFb)]/(NBMo-NBMras);
NBMo is the amount of the NBM in the heavy oil; NBMb is the amount of the
NBM in the blend; SASFb is the fraction of the separation-aid solvent in
the blend; and NBMras is the amount of the NBM in the recovery-aid
solvent.

5. The method of claim 1, wherein the NBM is a component that is
substantially present in the heavy oil and substantially lacking in the
recovery-aid solvent.

7. The method of claim 1, wherein the measurements are made using at
least one of X-Ray Fluorescence analyzer, Inductively Coupled Plasma
Emission Spectroscopy (ICPES), combustion fluorescence, ultraviolet
fluorescence, solvent precipitation of asphaltenes, and pyrolysis in
absence of oxygen.

9. The method of claim 1 further comprising the step of recovering, in a
solvent recovery process, at least a portion of the recovery-aid solvent
from the blend.

10. The method of claim 9, wherein the solvent recovery process is
selected from the group consisting of distillation, fractionation,
evaporation, and any combination thereof.

11. The method of claim 9 further comprising the step of adjusting at
least one step in the solvent recovery process in response to the
determined fraction of the recovery-aid solvent in the blend.

12. The method of claim 1, wherein a plurality of NBMs are used to
determine the fraction of the recovery-aid solvent.

13. The method of claim 1 further comprising the step of correlating the
determined fraction of the recovery-aid solvent in the blend to an
overall effectiveness of a solvent-based heavy oil production process,
wherein the blend is generated during the solvent-based heavy oil
production process.

14. The method of claim 13 further comprising the step of adjusting at
least one step in the solvent-based heavy oil production process in
response to the determined fraction of the recovery-aid solvent in the
blend.

15. A heavy oil production method, comprising: injecting a recovery-aid
solvent into a heavy oil formation to form an initial blend of the
recovery-aid solvent and heavy oil; recovering the initial blend from a
reservoir using a solvent-based production process; recovering, in a
solvent recovery process, at least a portion of the recovery-aid solvent
from the initial blend to form a partially recovered blend; and applying
a solvent surveillance method to the partially recovered blend, the
solvent surveillance method comprising: (a) measuring an amount of a
native bitumen marker (NBM) in the heavy oil; (b) measuring an amount of
the NBM in the recovery-aid solvent; (c) measuring an amount of the NBM
in the partially recovered blend; and (d) applying a blending model to
determine a fraction of the recovery-aid solvent in the partially
recovered blend.

16. The method of claim 15, wherein the blending model is at least
partially described by formula: the fraction of the recovery-aid solvent
in the partially recovered blend=(NBMo-NBMb)/(NBMo-NBMras); wherein NBMo
is the amount of the NBM in the heavy oil, NBMb is the amount of the NBM
in the partially recovered blend, NBMras is the amount of the NBM in the
recovery-aid solvent.

17. The method of claim 16, wherein the fraction of the recovery-aid
solvent and the amounts of the NBM are all measured in a unit selected
from the group consisting of weight fraction, mole fraction, volume
fraction, parts per million by volume, and parts per million by weight.

18. The method of claim 15, further comprising blending a separation-aid
solvent with at least one of the initial blend and the partially
recovered blend; and the solvent surveillance method further including
determining a fraction of the separation-aid solvent in the partially
recovered blend, wherein: the blending model is at least partially
described by formula: the fraction of the recovery-aid solvent on a
separation-aid solvent free basis in the partially recovered
blend=[NBMo-NBMb*(1/(1-SASFb)]/(NBMo-NBMras); NBMo is the amount of the
NBM in the heavy oil; NBMb is the amount of the NBM in the partially
recovered blend; SASFb is the fraction of the separation-aid solvent in
the partially recovered blend; and NBMras is the amount of the NBM in the
recovery-aid solvent.

19. The method of claim 15, further comprising adjusting at least one
step in the solvent recovery process in response to the determined
fraction of the recovery-aid solvent in the partially recovered blend.

20. The method of claim 15 wherein a plurality of NBMs are used to
determine the fraction of the recovery-aid solvent.

21. The method of claim 15, wherein the NBM is an element that is
substantially present in the heavy oil and substantially lacking in the
recovery-aid solvent.

23. The method of claim 15, wherein the measurements are made using at
least one of an X-Ray Fluorescence analyzer, an Inductively Coupled
Plasma Emission Spectroscopy (ICPES), combustion fluorescence,
ultraviolet fluorescence, solvent precipitation of asphaltenes, and
pyrolysis in absence of oxygen.

25. The method of claim 15, wherein the solvent recovery process is
selected from the group consisting of distillation, fractionation,
evaporation, membrane separation, and any combination thereof.

26. The method of 15 further comprising the step of relating the fraction
of the recovery-aid solvent to an overall effectiveness of the solvent
recovery process.

27. The method of claim 15 wherein the solvent surveillance method is
applied to a plurality of samples of the partially recovered blend to
minimize an effect of variations in concentration of the NBM in at least
one of the heavy oil and the recovery-aid solvent.

28. The method of claim 15 further comprising adjusting at least one step
in the solvent-based production process in response to the determined
fraction of the recovery-aid solvent in the partially recovered blend.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent
Application 61/267,119 filed 7 Dec. 2009 entitled SOLVENT SURVEILLANCE IN
SOLVENT-BASED HEAVY OIL RECOVERY PROCESSES, the entirety of which is
incorporated herein by reference in its entirety.

[0003] This section is intended to introduce various aspects of the art,
which may be associated with exemplary embodiments of the presently
disclosed invention. This discussion is believed to assist in providing a
framework to facilitate a better understanding of particular aspects of
the presently disclosed invention. Accordingly, it should be understood
that this section should be read in this light, and not necessarily as
admissions of prior art.

[0004] Various methods are used in the recovery of deeply buried heavy oil
or bitumen deposits within oil-sands reservoirs. In situ heavy oil or
bitumen recovery techniques are applied to indigenous resource that
cannot be mined economically because of the depth of the overburden. It
is recognized that in situ methods disturb considerably less land and
therefore require less land-reclamation activity than mining projects. In
general, the focus of in situ heavy oil or bitumen recovery processes is
to reduce the viscosity of the heavy oil or bitumen to enable it to be
produced from a well and transported by pipeline or other means. One
method of reducing the viscosity of the heavy oil or bitumen is to
introduce a recovery-aid solvent, such as by reservoir injection, into
the heavy oil or bitumen. Such a process may be referred to as a
solvent-based recovery process (such as Cyclic Solvent Process, Hot
Solvent Process, and Vapor Extraction). A second method of reducing
viscosity of the heavy oil or bitumen is to introduce the recovery-aid
solvent along with other viscosity reducing agents including but not
limited to, steam, hot water or hot gases. Such a process may also be
referred to as a solvent-based recovery process (such as Expanding
Solvent Steam Assisted Gravity Drainage, Solvent Assisted Steam Assisted
Gravity Drainage, Liquid Addition to Steam for Enhanced Recovery, and
Solvent Steam Assisted Vapor Extraction).

[0005] Upon recovery, the heavy oil/bitumen is generally in the form of an
emulsion containing the recovery-aid solvent as well as water. To
separate the water from the emulsion, a separation-aid solvent is
generally added to facilitate the separation of the water through density
and viscosity reduction.

[0006] One challenge in any solvent-based recovery process is the accurate
determination of the amount (e.g., mass, volume, percentage, and the
like) of the recovery-aid solvent that is recovered from the reservoir
along with the heavy oil/bitumen. An accurate accounting of the
recovery-aid solvent may be beneficial, for example, in maintaining
desirable environmental conditions, determining the efficiency of the
recovery process, determining the appropriate processing of the emulsion,
obtaining regulatory approval to develop a heavy oil/bitumen project,
and/or assessing the economic feasibility of a given solvent-based
recovery process.

[0007] Conventional methods of measurement of recovery-aid solvent rely on
gas chromatography (GC), Fourier Transform Infrared spectroscopy (FTIR),
thermogravimetry (TG), solvent evaporation, density measurements, or
viscosity measurements. Because of inaccuracies and impreciseness of the
other methods, GC is the most preferred conventional method. However, the
GC method is not accurate because the boiling ranges of the heavy
components in the solvent overlap with the light components in the
recovered crude. Also, the reliability of the GC process may not be
optimal due to the potential for contamination of the GC column by
non-eluted heavy oil/bitumen.

[0008] As such, there is still a substantial need for an improved system
and method for determining the amount of a recovery-aid solvent in the
recovery-aid solvent diluted heavy oil/bitumen that is produced from a
reservoir.

SUMMARY

[0009] One embodiment discloses a method of solvent surveillance. The
method comprises the steps of measuring an amount of a native bitumen
marker (NBM) in a heavy oil, measuring an amount of the NBM in a
recovery-aid solvent, measuring an amount of the NBM in a blend of at
least the heavy oil and the recovery-aid solvent, and applying a blending
model to determine the fraction of the recovery-aid solvent in the blend.

[0010] In at least one exemplary embodiment, the blending model is at
least partially described by formula: the fraction of the recovery-aid
solvent in the blend=(NBMo-NBMb)/(NBMo-NBMras); wherein NBMo is the
amount of the NBM in the heavy oil, NBMb is the amount of the NBM in the
blend, and NBMras is the amount of the NBM in the recovery-aid solvent.

[0011] In the above formula, the amount of NBM in the blend is on a
separation-aid solvent free basis. However, in one or more embodiments, a
separation-aid solvent, such as toluene, may be added to the sampled
emulsion to remove water, leaving a hydrocarbon blend composed primarily
of heavy oil/bitumen, separation-aid solvent and recovery-aid solvent.
This hydrocarbon sample containing the separation-aid solvent may then be
analyzed for the recovery-aid solvent. In such an embodiment, the amount
of NBM in the blend may be measured in the presence of the separation-aid
solvent. However, the NBM in the heavy oil and the recovery-aid solvent
are generally measured separately and reported on a separation-aid
solvent free basis. As such, the method may include the step of modifying
the blending formula to include the fraction of a separation-aid solvent
in the blend, which is generally known. The blending model may then be at
least partially described by the formula: the fraction of the
recovery-aid solvent in the blend (on a separation-aid solvent free
basis)=[NBMo-NBMb*(1/(1-SASFb))]/(NBMo-NBMras); wherein NBMo is the
amount of the NBM in the heavy oil, NBMb is the amount of the NBM in the
blend including the separation-aid solvent, NBMras is the amount of the
NBM in the recovery-aid solvent, SASFb is the fraction of the
separation-aid solvent in the blend.

[0012] Another embodiment discloses a heavy oil production method
comprising the steps of injecting a recovery-aid solvent into a heavy oil
formation via, for example, a reservoir and using, for example, a
solvent-based heavy oil production process to form an initial blend of
the recovery-aid solvent and heavy oil; producing (i.e., recovering) the
initial blend from the reservoir; recovering, in a solvent recovery
process, at least a portion of the recovery-aid solvent from the initial
blend to form a partially recovered blend; and applying a solvent
surveillance method to the partially recovered blend. One or more
embodiments of the heavy oil production method may apply one or more of
the solvent surveillance methods and/or blending models previously
described in this section.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The foregoing and other advantages of the present invention may
become apparent upon reviewing the following detailed description and
drawings of non-limiting examples of embodiments in which:

[0014] FIG. 1A is a flow diagram of a method of solvent surveillance
according to an embodiment of the present invention;

[0015] FIG. 1B is a flow diagram of a heavy oil production method
according to an embodiment of the present invention;

[0016]FIG. 2 illustrates a solvent-based heavy oil/bitumen production
process with solvent surveillance in accordance with a first embodiment
of the invention;

[0017]FIG. 3 illustrates another solvent-based heavy oil/bitumen
production process with solvent surveillance in accordance with a second
embodiment of the invention;

[0018]FIG. 4 illustrates an automatic control system for solvent
surveillance according to an embodiment of the invention;

[0019] FIG. 5 illustrates a block diagram of a computer environment which
may be implemented as part of an embodiment of the present invention;

[0020]FIG. 6 is a diagram of test data illustrating the relationship
between different native bitumen markers and the concentration of a
solvent in a solvent/heavy oil blend;

[0021]FIG. 7 is a simulation data plot illustrating the distribution of
sulfur in bitumen generated by Latin-Hypercube sampling;

[0023] In the following detailed description section, some specific
embodiments of the present invention are described in connection with
preferred, alternative, and exemplary embodiments. However, to the extent
that the following description is specific to a particular embodiment or
a particular use of the present invention, this is intended to be for
illustrative purposes only and simply provides a description of the
particular embodiments. Accordingly, the invention is not limited to the
particular embodiments described below, but rather, it includes all
alternatives, modifications, and equivalents falling within the true
spirit and scope of the appended claims.

Definitions

[0024] Various terms as used herein are defined below. To the extent a
term used in a claim is not defined below, it should be given the
broadest definition persons in the pertinent art have given that term.

[0025] As used herein, the "a" or "an" entity refers to one or more of
that entity. As such, the terms "a" (or "an"), "one or more", and "at
least one" can be used interchangeably herein unless a limit is
specifically stated.

[0026] As used herein, the term "heavy oil" refers to hydrocarbon fluids
that are highly viscous at ambient conditions (e.g., 15 deg. C and 1 atm
pressure). Heavy oil may include carbon and hydrogen, as well as smaller
concentrations of sulfur, oxygen, and/or nitrogen. As used in this
application, heavy oil may include any hydrocarbon fluid having API
gravity lower than about 20 degrees such as, but not limited to, bitumen,
de-asphalted bitumen, tar and/or asphalt.

[0027] As used herein, the term "bitumen" refers to a non-crystalline
solid or viscous hydrocarbon material that is substantially soluble in
carbon disulfide, toluene, xylene or methylene chloride. The terms
bitumen and heavy oil are used interchangeably throughout this
disclosure.

[0028] As used herein, the term "recovery-aid solvent" refers to alkanes,
such as methane, ethane, propane, butane, pentane, hexane, heptane and
other higher molecular weight alkanes, alkenes, naphthenes, aromatics or
mixtures thereof, which when blended with bitumen reduces its viscosity.
Recovery-aid solvent may also include gas plant condensates, which are
mixtures of alkanes, alkenes, naphthenes and aromatics.

[0029] As used herein, the term "NBM" means native bitumen markers, which
are any measurable elements (e.g., S, V or Ni) or components (such as
asphaltenes, CCR or MCR) that are naturally present in bitumen in
substantial amounts and are not present in substantial amounts in
solvent.

[0030] As used herein, the term "asphaltenes" means components of bitumen
that precipitate out in the presence of substantial amount of solvents,
such as n-pentane, n-hexane or n-heptane, and are described as
nC5-asphaltenes, nC6-asphaltenes or nC7-asphaltenes, respectively.

[0031] As used herein, the term "MCR" means the microcarbon residue as
determined by ASTM D4530.

[0032] As used herein, the term "CCR" means Conradson carbon reside as
determined by ASTM D189.

[0033] As used herein, the terms "comprising," "comprises," and "comprise"
are open-ended transition terms used to transition from a subject recited
before the term to one or more elements recited after the term, where the
element or elements listed after the transition term are not necessarily
the only elements that make up the subject.

[0034] As used herein, the terms "containing," "contains," and "contain"
have the same open-ended meaning as "comprising," "comprises," and
"comprise."

[0035] As used herein, the terms "having," "has," and "have" have the same
open-ended meaning as "comprising," "comprises," and "comprise."

[0036] As used herein, the terms "including," "includes," and "include"
have the same open-ended meaning as "comprising," "comprises," and
"comprise."

[0037] As used herein, the term "solvent-based production process" means a
process that uses recovery-aid solvent to produce heavy oil as a heavy
oil-solvent blend.

[0038] As used herein, the term "solvent recovery process" means a process
that recovers solvent, at least partially, from a heavy oil-solvent
blend.

[0039] As used herein, the term "blend" means a mixture of heavy oil and
recovery-aid solvent which may contain free water and/or emulsified
water.

Description

[0040] With reference to the figures, wherein like reference numbers
indicate like elements, embodiments of the present invention are
described for providing improved surveillance of a solvent (i.e., a
recovery-aid solvent) used in connection with recovery of heavy oil.
Unless specifically stated otherwise, subsequent uses of the term
"solvent" refer to a recovery-aid solvent; as opposed to a separation-aid
solvent.

[0041] More specifically, one or more native bitumen markers (NBMs) are
measured and a blending model is applied to determine a fraction (i.e.,
amount) of a solvent in a blend of heavy oil and solvent. One or more
embodiments of the present invention may also provide for the adjustment
of one or more steps involved in the recovery or post recovery processing
of the heavy oil. As used in this application, the term "heavy oil" will
be used interchangeably with "bitumen" and will refer to any appropriate
hydrocarbon material that satisfies either definition, as specified in
the Definitions section of this application, and/or would be recognized
as a heavy oil or bitumen by one of ordinary skill in the art. For
example, the term heavy-oil includes partially and/or completely
de-asphalted bitumen such as may be produced through solvent-based
extraction operations. The partially or completely de-asphalted bitumen,
which may be referred to as maltene, may be a result of asphaltene
precipitation in the formation or wellbore and/or a result of operations
on the surface. In addition, the measured NBM may be any component
suitable for distinguishing the heavy oil from solvent. Preferably, the
NBM is a component that is substantially present in heavy oil and
substantially lacking in the solvent of interest; for example sulfur (S),
nickel (Ni), vanadium (V), chromium (Cr), micro-carbon residue (MCR),
Conradson carbon residue (CCR), nC5-asphaltenes, nC6-asphaltenes or
nC7-asphaltenes.

[0042] Referring to FIG. 1A, a flow diagram of a method 100 of solvent
surveillance according to an embodiment of the present invention is
shown. The method 100 generally includes a plurality of blocks or steps
that may be performed serially. As will be appreciated by one of ordinary
skill in the art, the order of the steps shown in FIG. 1A is exemplary
and the order of one or more steps may be modified within the spirit and
scope of the present invention. Additionally, the steps of the method 100
may be performed in at least one non-serial (or non-sequential) order,
and one or more steps may be omitted to meet the design criteria of a
particular application. Step 102 represents an entry point into the
method 100.

[0043] At step 104, the NBM in the heavy oil is measured. In at least one
embodiment, one or more samples of the heavy oil are extracted from one
or more wells associated with the heavy oil recovery site. In such an
embodiment, the NBM of the heavy oil may be determined by analyzing the
one or more samples. Similarly, at steps 106 and 108, the NBM of the
solvent and the blend (e.g., the heavy oil and solvent blend which has
been extracted from a reservoir), respectively, are measured.

[0044] As is well understood, the asphaltene components of the heavy oil
in the reservoir are susceptible to precipitation depending on the nature
and quantity of solvent injected into the reservoir. When such asphaltene
precipitation does occur, or is prone to occur, it may be difficult to
control the degree of precipitation, or the degree to which the heavy oil
is de-asphalted. In such implementations, the measurement of the heavy
oil NBM may include completely de-asphalting the heavy oil to provide a
consistent basis. The heavy oil may be de-asphalted through any
conventional techniques implemented either in the formation or on the
surface. The NBM of the de-asphalted heavy oil may then be measured to
complete step 104. Similarly, in implementations where the produced heavy
oil is at least partially de-asphalted, it will be recognized that the
NBM of the blend, at step 108, is measured after completely de-asphalting
the solvent and heavy oil blend. Accordingly, the heavy oil NBM, at 104,
and the blend NBM, at 108, are measured on a consistent basis, either
with all of the naturally occurring asphaltene components or with them
all removed.

[0045] Step 109 represents the optional step of determining a fraction of
a separation-aid solvent. This may be done by adding a known amount of
the separation-aid solvent to the known amount of the produced emulsion
sample, centrifuging the emulsion and then determining the amount of the
total hydrocarbon (heavy oil, recovery-aid solvent and separation-aid
solvent) separated, and assuming that all the separation-aid solvent is
in the total hydrocarbon. Separation-aid solvents will be discussed
further in connection with step 110.

[0046] While steps 104, 106, and 108 refer to "measurement", it should be
appreciated that an amount of a NBM may be determined either directly,
such as by direct testing/observation of a sample of the relevant
substance, or indirectly, such as by calculation or estimation. In the
case of direct testing/observation, any suitable
method/apparatus/technology may be used such as one or more of: an X-Ray
Fluorescence analyzer (for S, Ni and V), Inductively Coupled Plasma
Emission Spectroscopy (ICPES) (for Ni and V), combustion fluorescence
(for S), ultraviolet fluorescence (for S), asphaltenes by solvent
precipitation, and MCR by pyrolysis in absence of oxygen. Likewise, any
appropriate unit of measure may be used such as weight fraction, mole
fraction, volume fraction, and parts per million (by volume or weight).

[0047] At step 110, an appropriate blending model is applied to the
measured NBM values to generate an output which corresponds to the amount
of recovery-aid solvent in the blend. In at least one embodiment, the
blending model is at least partially described by the formula:

the fraction of the recovery-aid solvent=(NBMo-NBMb)/(NBMo-NBMras)

[0048] where:

[0049] NBMo=the amount of a given NBM in the heavy oil

[0050] NBMb=the amount of the given NBM in the blend

[0051] NBMras=the amount of the given NBM in the recovery-aid solvent

[0052] In the above formula, each of the amount of NBM in the blend, heavy
oil and solvent is expressed on a separation-aid solvent free basis. In
practice, a separation-aid solvent, such as toluene, may be added to the
blend to remove water. As such, it may be necessary and/or advantageous
to measure (e.g., at step 108) the amount of NBM in the blend containing
the separation-aid solvent. The NBM in the heavy oil and the recovery-aid
solvent may be measured separately on a separation-aid solvent free
basis. The blending model for determining the fraction of the
recovery-aid solvent in the blend when separation-aid solvent is present
may be at least partially described by the formula:

the fraction of the recovery-aid solvent in the blend on a
separation-aid solvent free basis=[NBMo-NBMb*(1/(1-SASFb)]/(NBMo-NBMras)

[0053] where:

[0054] NBMo=the amount of a given NBM in the heavy oil

[0055] NBMb=the amount of the given NBM in the blend including the
separation-aid solvent

[0056] NBMras=the amount of the given NBM in the recovery-aid solvent

[0057] SASFb=the fraction of the separation-aid solvent in the blend

[0058] While the above exemplary formula can be used when accounting for
the separation-aid solvent, any appropriate blending model may be
implemented to satisfy the design criteria of a particular embodiment.
For example, similar modifications of the formula may be implemented to
account for de-asphalted heavy oil, as discussed above. Furthermore, one
or more specific embodiments of the present invention may include one or
more iterations of the steps 104, 106, 108, 109 and/or 110. In such an
embodiment, each iteration may measure a different NBM; that is, a
different NBM may be selected for each iteration. Such an iterative
process may increase the accuracy of the determined amount of solvent.
Similarly, a plurality of NBMs may be used to increase the accuracy of
the determination of the solvent fraction.

[0059] As illustrated in FIG. 1A, the method 100 may, depending on the
particular application, include one or more additional steps (e.g., steps
112, 114, 116, 118, and/or 120). For example, at least one embodiment may
include the step of recovering, in a solvent recovery process, at least a
portion of the solvent from the blend of heavy oil and solvent (i.e.,
step 112). Similarly, optional step 114 includes adjusting at least one
step in a solvent recovery process (such as the solvent recovery process
of step 112) in response to the output of step 110; optional step 116
includes adjusting at least one step in a corresponding solvent-based
heavy oil production process in response to the output of step 110;
optional step 118 includes correlating the output of step 110 to an
overall effectiveness of a solvent-based heavy oil production process
(such as the process of step 116); and optional step 120 includes
correlating (i.e., relating) the output of step 110 to an overall
effectiveness of a solvent recovery process (such as the process of step
112).

[0060] Step 122 represents an exit point out of the method 100.

[0061] Referring now to FIG. 1B, a flow diagram of a heavy oil production
method 150 according to an embodiment of the present invention is shown.
Like the method 100, the method 150 generally includes a plurality of
blocks or steps that may be performed serially. As will be appreciated by
one of ordinary skill in the art, the order of the steps shown in FIG. 1B
is exemplary and the order of one or more steps may be modified within
the spirit and scope of the present invention. Additionally, the steps of
the method 150 may be performed in at least one non-serial (or
non-sequential) order, and one or more steps may be omitted to meet the
design criteria of a particular application. Step 152 represents is an
entry point into the method 150.

[0062] At step 154 a recovery-aid solvent is injected into the heavy oil
reservoir to form an initial blend that may contain water either as free
water and/or emulsified water. The initial blend is then recovered (i.e.,
produced), at step 156, from a corresponding reservoir using a
solvent-based production process such as: (i) Expanding Solvent Steam
Assisted Gravity Drainage ("ES-SAGD"); (ii) Solvent Assisted Steam
Assisted Gravity Drainage ("SA-SAGD"); (iii) Liquid Addition to Steam for
Enhanced Recovery ("LASER"); Vapor Extraction (VAPEX), Combined Vapor and
Steam Recovery ("SAVEX"); Cyclic Solvent Process ("CSP"), Hot Solvent
Process; or any combination thereof. As discussed above, the initial
blend may be de-asphalted through a variety of techniques to complete any
asphaltene precipitation that may have begun during the recovery. Step
158 includes recovering, in a solvent recovery process, at least a
portion of the solvent from the initial blend to form a partially
recovered blend. As illustrated at step 160, a solvent surveillance
method, such as the method 100 of FIG. 1A, may be advantageously
implemented in connection with the partially recovered blend of step 158.

[0063] Step 162 represents an exit point out of the method 150.

[0064] Referring to FIG. 2, a block diagram 200 of a solvent-based heavy
oil production process 226 with solvent surveillance in accordance with
an embodiment of the invention is provided. Element 202 represents a
heavy oil reservoir. In at least one embodiment, an injection well 206 is
drilled into the reservoir 202. The injection well 206 generally provides
a mechanism for injecting substances, such as solvents 208 and/or steam
(not shown), into the reservoir 202 for the purpose of reducing the
viscosity of the heavy oil 204 within the reservoir 202. The
viscosity-reduced blend (i.e., initial blend) 210 of heavy oil 204 and
solvent 208 may then be extracted using any appropriate process such as
one or more of the solvent-based production processes previously
discussed in connection with step 156 of FIG. 1B. The recovery process
226 generally includes a production well 212.

[0065] The blend 210, or a portion thereof, may then be processed using a
solvent recovery process 214 to produce a partially recovered blend 216
using any appropriate mechanism such as: (i) distillation, (ii)
fractionation, (iii) evaporation, (iv) membrane separation, or any
combination thereof. The partially recovered blend 216 may be
characterized by a reduction in the amount of solvent 208 as compared to
the initial blend 210. As such, the solvent recovery process 214 acts to
recover (i.e., separate, remove, etc.) at least a portion of the solvent
208 from the blend 210. Element 230 generally represents the recovered
solvent.

[0066] As further illustrated in FIG. 2, a solvent surveillance method
218, such as the method 100 described in connection with FIG. 1A, may be
performed on the blend 210. The method 218 may take the NBM of the heavy
oil 204, the NBM of the solvent 208 and the NBM of the blend 210 as
inputs 104', 106' and 108' respectively. In some implementations, as
previously discussed, measuring the NBM of the heavy oil 204 and the NBM
of the blend 210 may include measuring the NBM of the de-asphalted heavy
oil and blend. Optionally, the method 218 may take the fraction of a
separation-aid solvent as input 109'. In at least one embodiment, the
output 220, corresponding to the amount/fraction of solvent 208 in the
blend 210, of the solvent surveillance method 218 may be used to adjust
at least one step in the solvent recovery process 214. As such, the
output 220 may be used in connection with a feed-forward control loop 222
to the solvent recovery process 214. Similarly, an embodiment of the
present invention may use the output 220 to adjust at least one step in
the heavy oil production process 226. As such, the output 220 may be used
in connection with a feedback control loop 224. In yet another
embodiment, the output 220 may be correlated to an overall effectiveness
of the solvent-based heavy oil production process 226.

[0067] Turning now to FIG. 3, a block diagram 300 illustrating another
solvent-based heavy oil production process 226' with solvent surveillance
that may be implemented in connection with the present invention is
shown. The solvent surveillance method 218' generally takes the NBM of
the heavy oil 204, the NBM of the solvent 208 and the NBM of the
partially recovered blend 216 as inputs 104'', 106'' and 108''
respectively. Optionally, the method 218' may take the fraction of the
separation-aid solvent as input 109''. Accordingly, the process 300 may
be implemented similarly to the process 200 of FIG. 2 with the exception
that the solvent surveillance method 218', such as the method 100, is
performed on the partially recovered blend 216 instead of the initial
blend 210.

[0068] In accordance with at least one embodiment of FIG. 3, the output
220', corresponding to the amount/fraction of solvent in the partially
recovered blend 216, may be used to adjust at least one step in the
solvent recovery process 214. As such, the output 220' may be used in
connection with a first feedback control loop 302 to the solvent recovery
process 214 and/or correlated to an overall effectiveness of the solvent
recovery process 214. Similarly, one or more embodiments may use the
output 220' to adjust at least one step in the heavy oil production
process 226'. As such, the output 220' may be used in connection with a
second feedback control loop 304 and/or correlated to an overall
effectiveness of the heavy oil production process 226'.

[0069] While FIGS. 2 and 3 illustrate implementations where the solvent
surveillance is applied to either the produced blend 210 or the partially
recovered blend 216, the solvent surveillance methods and systems
described herein may be applied to any heavy oil stream or combinations
of heavy oil streams. For example, some implementations may apply the
present solvent surveillance methods and systems to both the produced
blend 210 and the partially recovered blend 216 and provide feedback
and/or feedforward control based on either or both streams. Such an
implementation may inform the operator regarding the effective recovery
of solvent from the formation and the effectiveness of the solvent
recovery process 214. In implementations where the partially recovered
blend 216 is sent for further processing, the present solvent
surveillance systems and methods may be applied to still further
downstream processes to determine the effectiveness of later solvent
recovery efforts.

[0070] Referring to FIG. 4, an automatic control system 400 for solvent
surveillance according to an embodiment of the present invention is
shown. The system 400 generally includes a control module (i.e.,
controller) 402 and may be advantageously implemented in connection with
the method 100 of FIG. 1A, the method 150 of FIG. 1B, the embodiment of
FIG. 2, the embodiment of FIG. 3 and/or any appropriate system and/or
method to meet the design criteria of a particular application. The
controller 402 may be a computer such as the computer environment
discussed in connection with FIG. 5 (below), an application specific
integrated circuit ("ASIC"), an electronic circuit, a processor (shared,
dedicated, or group) and memory that execute one or more software or
firmware programs, a combinational logic circuit, and/or other suitable
component(s) that provides the described functionality. It is
contemplated that all or part of the functionality of the components in
the controller 402 may be incorporated into a single module, such as
shown in FIG. 4. Alternatively, one or more functions of the controller
402 may be distributed among a plurality of modules (not shown).

[0071] The controller 402 may receive input signals (i.e., inputs) 404
using any appropriate mechanism to suit the design criteria of a
particular application. Each input 404 generally represents one or more
physical characteristic of real world materials and may, for example,
represent the amount of NBM in a corresponding (i) heavy oil, (ii)
solvent, or (iii) blend (initial, partially recovered, or otherwise). In
at least one embodiment, the input 404 may optionally represent the
determined fraction of a separation-aid solvent in a blend.

[0072] As illustrated in FIG. 4, the controller 402 may apply a blending
model 406, such as a blending model described in connection with step 110
of FIG. 1A, to the inputs 404 to determine a solvent fraction 408 of a
corresponding blend of solvent and heavy oil. It may be appreciated that
the solvent fraction 408 represents the real world physical
amount/concentration of solvent in the blend.

[0073] In at least one embodiment, the controller 402 is in electrical
communication with a computer readable medium 410. The computer readable
medium 410 may be any appropriate mechanism for storing and retrieving
electronic instructions 412 such as a magnetic medium (e.g., a disk or
tape); a magneto-optical or optical medium (e.g., a disk); a solid state
medium (e.g., a memory card) as well as art-recognized equivalents and
successor technologies. In addition, the medium 410 may be physically
integrated with the controller 402, as illustrated in FIG. 4, remotely
located from the controller 402 (not shown), or a combination thereof.
The medium (i.e., media) may include one or more set of instructions 412.
Each set of instructions 412 may comprise one or more individual
instructions for generating one or more output signals 414 based at least
in part on the solvent fraction 408.

[0074] As illustrated in FIG. 4, an output signal 414 may be implemented
to control at least one step in a solvent recovery process, such as the
solvent recovery process 214. Similarly, an output signal 414 may be
implemented to control at least one step in a solvent-based heavy oil
production process, such as the production processes 226 and/or 226'. In
yet another embodiment, an output signal 414 may correlate the determined
solvent fraction 408 to an effectiveness of a corresponding solvent-based
production process (such as the production processes 226 and/or 226'), a
corresponding solvent recovery process (such as the recovery process
214), and/or the like.

[0075] Referring now to FIG. 5, there is illustrated a block diagram of a
computer environment 500 that may be advantageously implemented in
connection with the method 100 of FIG. 1A, the method 150 of FIG. 1B, the
processes of FIGS. 2 and 3, and/or the controller 402 of FIG. 4. In
general, FIG. 5 and the following discussion are intended to provide a
brief description of a suitable computing environment 500 in which the
various aspects of the claimed subject matter may, if advantageous for a
particular application, be implemented.

[0076] With reference again to FIG. 5, the exemplary environment 500 may
include a system computer 512, which may be implemented as any
conventional personal computer or workstation, such as a UNIX-based
workstation. The system computer 512 may be in electronic communication
with data storage devices 510, 514, and 516 (e.g., disk storage devices)
which may be external storage devices, internal storage devices, or a
combination of internal and external storage devices. Electronic
communication between external storage devices and the system computer
512 may be established via any suitable mechanism such as via a local
area network, USB cable, parallel data cable, serial data cable, firewire
cable, and/or remote access. Of course, while storage devices 510, 514,
and 516 are illustrated as separate devices, a single storage device may
be used to store any and all of the corresponding information (e.g.,
program instructions, data, and results) as desired.

[0077] In one embodiment, the input data are stored in storage device 514.
The system computer 512 may retrieve the appropriate data from the
storage device 514 to perform operations according to program
instructions that correspond to the methods described herein. The program
instructions may be written in a computer programming language, such as
C++, Java and the like. The program instructions may be stored in a
computer-readable memory, such as program storage device 516. Of course,
the memory medium storing the program instructions may be of any
conventional type used for the storage of computer programs, including
hard disk drives, floppy disks, CD-ROMs and other optical media, magnetic
tape, and the like.

[0078] According to an embodiment, the system computer 512 presents output
onto graphics display 506, or alternatively via printer 508. The system
computer 512 may store the results of the methods described above on
storage device 510, for later use and further analysis. The keyboard 504
and the pointing device (e.g., a mouse, trackball, or the like) 502 may
be provided with the system computer 512 to enable interactive operation
with an operator. The system computer 512 may be located at a data center
remote from the corresponding reservoir (such as the reservoir 202 of
FIGS. 2 and 3).

[0079]FIG. 6 is a diagram of test data illustrating the relationship
between different NBMs and the concentration of a solvent, such as 208,
in a solvent/heavy oil blend, such as 210 and/or 216. More specifically,
the amount of nickel (Ni) and vanadium (V), measured in parts per million
on the left Y-axis, are plotted against the solvent concentration, in
weight percent solvent, on the X-axis. In this particular example the
solvent may be a gas plant condensate. R2 in the plot indicates the
correlation coefficient between the known and NBM-measured solvent
concentration; an R2 closer to 1 indicating an excellent fit. The
resulting plots illustrate a substantially linear relationship between
these NBMs and the concentration of a corresponding solvent in a blend.
Similarly, the amount of sulfur (S) and micro-carbon residue (MCR),
measured in parts per million on the right Y-axis, are plotted against
the solvent concentration, in weight percent solvent, on the X-axis. The
resulting plots also illustrate a substantially linear relationship
between the two NBMs and the concentration of a corresponding solvent in
a blend.

[0080] In practicing one or more embodiments of the present invention, one
may encounter variation in bitumen NBM properties with time. If the
variation is random, the effect on the cumulative solvent accounted for
will generally be minimal, especially if the number of samples taken for
NBM measurements is large. The number of samples needed to achieve
certain accuracy may be estimated by performing a statistical simulation
using known distribution in the variation of each NBM. The steps involved
in the simulation may include:

[0081] (a) generating multiple samples with different values of each
bitumen NBM using its known probability distribution and Monte-Carlo or
Latin Hypercube sampling. Latin Hypercube sampling is preferred to
Monte-Carlo sampling as the former requires fewer samples to reproduce
the chosen distribution. An example of a distribution generated for
bitumen sulfur using Latin Hypercube sampling is shown in FIG. 7.

[0082] (b) generating a "measured" blend NBM using a known recovery-aid
solvent fraction and an appropriate blending model such as the model
described in connection with method 100.

[0083] (c) adjusting the recovery-aid solvent fraction until the sum of
squares of the differences between "measured" and predicted NBM
calculated by using the blending model is minimized. A weighted
regression, in which the weights are inversely proportional to the
variance in the NBM may be used to improve estimation of the best-fit
"analyzed" solvent fraction.

[0084] FIGS. 8(A-C) show the simulation results for 125 (˜2 samples
per week), 250 (˜4 samples per week) and 500 (˜7 samples per
week) samples, respectively, for a typical SA-SAGD operation. As the
sample number increases, the % difference between "analyzed" and known
cumulative solvent volume decreases. These figures also suggest that the
accuracy may be further improved through increased sampling at the early
stages of production from a well.

[0085] For a given reservoir, the NBM variation in bitumen can be
determined and taken into account in the solvent fraction determination
by measuring the bitumen in the core samples from different parts of the
reservoir.

[0086] In a typical SA-SAGD application, the NBM variation in bitumen may
generally be handled by taking bitumen samples during the warm-up period
of the process (when solvent typically is not injected or produced) and
analyzing the bitumen for NBM.

[0087] In an SA-SAGD piloting, NBM variation in bitumen can be determined
by taking samples from the portion of the test where only steam is
injected and determining the NBM in the bitumen without the solvent.

[0088] Similarly, the variation in solvent NBM can be taken into account
by taking samples of injected solvent at different times and adjusting
the blending model accordingly.

[0089] As may be appreciated, then, the present invention represents an
improvement in solvent surveillance for solvent-based heavy oil recovery
processes. The present invention may be susceptible to various
modifications and alternative forms, and the exemplary embodiments
discussed above have been shown only by way of example. It should again
be understood that the invention is not intended to be limited to the
particular embodiments disclosed herein. Indeed, the present invention
includes all alternatives, modifications, and equivalents falling within
the true spirit and scope of the appended claims.